Root

Development and Morphology

Origin• Derived from the hypocotyl of the

seed embryo• Developing from the radicle

(rudimentary tip)

Functions:1.Absorption

2.Anchorage

3.Conduction and storage

Morphology

root system

Radicle is not persistent

Hypocotyl

radicle Primary root Sec root Other roots

Tap root Fibrous root

Dicot

seedling

Primary root2dary root

3try rootRoot hair

Root system

Monocot seedling

epicotyl

Primary root

Root Development

Primary plant body

Root Structure

Characteristics: External

1.No leaves , leaf scars

2.No buds (axillary or apical)

Root Structure

Characteristics: Internal1. Arrangement of the protoxylem

exarch - centripetal differentiation of the protoxylem

2. Type of stele a. siphonostele - ring of vascular tissues surrounding a parenchymatous pithb. protostele – lobed and a solid core of primary xylem at the center

3. Number of primary xylem lobes formed by the procambiuma. diarch (2 xylem poles)b. triarch ( 3 )c. tetraarch (4)d. polyarch (many)

Root Structure1. Root tip – root cells are covered and grow and

push its own meristem towards the root cap

a. root cap

1. columella cells

2. Peripheral cells

b. Quiescent center

2. Subapical region

a. cellular division

b. celllular elongation

c. cellular maturation

3. Mature region

Columella cells contain amyloplast that sediment in response to gravity on the lower portion of the cells

Peripheral cells – came from columella cells, which secrete mucigel from the dictyosomes

Mucigel contains sugars, organic acids, vitamins, enzymes and amino acids

Functions: Protection, lubrication, water and nutrient absorption

Quiescent center - inactive cells arrested on the G1 phase of cell cycle, divides every 15 – 20 days

-Not affected by radiation ( differs from meristematic cells), - begins division to re – form the meristem

-Function: reservoir to replace damaged cells of the meristem ; - organize the pattern of primary growth in roots

Peripheral cells

Columella cells

Quiescent center

Apical meristemAllium root tip

Corn root tip

Root cap

protoderm

Ground meristem

procambium

Apical meristem

Region of differentiation Lateral maturation

stele

cortex

23

29

Allium root tip Corn root tip

epidermis

cortex

stele

metaxylem

endodermis

phloem

Endodermis

Cross section of Zea root

Specialized roots

1. Photosynthetic roots

2. Supporting roots (prop, brace, buttress, clinging)

3. Breathing roots (pneumatophores)

4. Reproductive roots (suckers)

5. Storage roots (root tubers)

6. Contractile roots

7. Absorptive roots (velamen, uncutinized epidermis)

8. Parasitic roots (mycorrhizae)

9. Nitrogen – fixing roots (root nodules)

Corn rootsBamboo roots

Root nodules

Physiological Effects of Roots

Factors affecting the rate of absorption in roots1. Temperature

2. Osmotic potential of the soil solution

a. gravel b. sand c. silt d. clay

3. Aeration (O2)

4. Concentration of CO2

5. Availability of water

a. gravitational water

b. capillary water

c. hygroscopic water

d. run – off water

Roots containing drugs

• Ginseng (Panax quinquefolia) – adaptogen• Pomegranate (Punica granatum) – anthelmintic• Countess bark (Cinchona succirubra) – anti – malaria,

anti – arrythmia• Ipecac (Cephaelis ipecacuanha) – anti – emetic,

expectorant• Monkshood (Aconitum napellus) – cardiac depressant• Mandrake (Podophyllum peltatum) - treatment of

small - cell lung cancer, testicular cancer, lymphomas, leukemias

• Rhubarb (Rheum officinale) – purgative• Yam (Dioscorea mexicana) – source of corticosteroids